Rotors for dynamoelectric machines, including motors and generators, have been constructed in many different ways in the prior art. One such construction well known in the prior art comprises a sintered iron core mounted to a shaft, the core being generally cylindrical, with one or more annular magnetic sleeves glued to the exterior of the core and surrounded. After being assembled, the core is magnetized in the desired manner to produce a permanent magnet rotor. However, because of the nature of this construction, tight manufacturing tolerances must be imposed and maintained to assure acceptable rotors after the components have been assembled and glued. As can be appreciated, the inner diameter of the annular sleeve must be such that it can be slip fitted over the sintered core and yet provide some space between the sleeve and core for the insertion of glue. However, to achieve true concentricity of the sleeve and shaft, it is desirable to limit the space between the sleeve and core to a minimum. Therefore, if the sleeve is too small for its matching core, it will not slip fit onto the core, or too small a space remains for an adequate amount of glue to be applied to secure the sleeve to the core. Alternatively, if the sleeve is too large, the sloppy fit between the sleeve and core can permit the sleeve to move out of concentricity with the core and shaft which can make the rotor unacceptable for use in a completed device. Of course, it can be very costly to impose and maintain tight manufacturing tolerances, and these extra costs can make a critical difference in small motors or generators which is typically where this type of rotor construction is used. Furthermore, care must be taken in assembling the sleeve to the core and if there is extra equipment or an extra step required in holding the sleeve concentric to the shaft while the glue is applied and cured, this can also increase the cost of manufacture.
To solve these and other problems in manufacturing a small rotor, the inventor herein has succeeded in developing an annular sleeve with a plurality of evenly spaced ridges along the inner surface of the sleeve, the ridges extending longitudinally and substantially parallel to the central axis. Interspaced between these ridges is a plurality of longitudinally extending and axially aligned grooves cut into the inner surface of the sleeve.
By the addition of the ridges along the inner surface of the sleeve, the inventor has succeeded in greatly relaxing the manufacturing tolerance for the sleeve as matched to the core. For example, if the sleeve is perfectly made to match the core, the core will fit snugly against the tops of the ridges, and all of the space between adjacent ridges and the spaces defined by the grooves are available for the application of glue to firmly affix the sleeve to the core. As the ridges are substantially the same height, they hold the sleeve in true concentricity with the core and shaft, as is desired. If the sleeve should be manufactured slightly smaller than optimal for its matching core, then the sleeve is sufficiently flexible or resilient such that the arc of sleeve between adjacent ridges slightly deforms or flattens against the core along its inner surface. This thereby permits assembly of a sleeve which is essentially too tight for its matching core and which would not fit the core if constructed in accordance with the teachings of the prior art. Furthermore, not only does the tight sleeve slip fit onto the core, but it exhibits true concentricity with the shaft and core because the sleeve is constructed of the same material throughout and the deformation between adjacent ridges is substantially the same. By using a large number of ridges, and because of the thickness of the sleeve, the amount of deformation is negligible along the outer surface of the sleeve such that it is not significantly distorted to detract from the operation of the rotor when assembled into a dynamoelectric machine. The ridges need not have a significant height to significantly relax the manufacturing tolerance of the sleeve. Therefore, this deformation effect is minimal when compared with other manufacturing tolerances of the device.
Still another advantage of the ridges is that the sleeve is self-centering as it is slipped onto the core, and it is held in a centered or concentric orientation automatically throughout the gluing and curing process. This completely eliminates the step in the prior art of holding the sleeve in concentric orientation with the core as the glue is applied and cured. For those rotors constructed without this step, the rotor of the present invention exhibits a reliably concentric core throughout the manufacturing run, something which was not easily achieved with the rotors of the prior art design.
The intermediate grooves serve the purpose of providing space along the entire length of the sleeve to receive adhesive even in the case when the sleeve is fully deformed between ridges and tightly pressed against the core. Thus, the grooves ensure that the sleeve is adequately secured to the core regardless of the fit of the sleeve to the core.
The foregoing has been a brief description of the principal advantages and features of the present invention. The invention may be more fully understood and appreciated by referring to the drawings and description of the preferred embodiment which follows.